Automotive GPS receivers for navigation are characterised by a large vertical LCD display and tend to be relatively thin in depth. The most commonly used antenna element is the rectangular ceramic patch antenna. These work well, provided they are large enough, and they are designed for efficient reception of right hand circularly polarised (RHCP) signals from the GPS satellite constellation. Ceramic patch antennas also need to be deployed substantially horizontally to work well. This means that a typical patch 25×25 mm or 17×17 mm square cannot be incorporated directly into the housing unless the housing is made very deep. An alternative solution is to use a hinged external patch antenna that may be flipped up into the horizontal position, as shown in FIG. 1a of the drawings. This is both mechanically awkward and expensive. Ceramic patches smaller than 17×17 mm exist but they perform less well and do not have such a good response to RHCP signals.
It is known from US 2003/0146874 to provide an antenna having a radiating structure in the form of a circular arc. The method of operation relies on the presence of a parasitic conductor. The driven element has a connection point close to ground which is referred to as the ‘neutral electrode’, which is stated to allow all currents of a quarter-wavelength to be distributed over the radiating element, and thus to have the effect of maximizing radiant efficiency (gain characteristics). If the neutral electrode is not provided, the currents of a quarter-wavelength are distributed to the radiating element and first connecting electrode, reducing current components in the radiating element and lowering the radiant efficiency (gain characteristics) to some extent.
There is no discussion as how the position of the ‘neutral electrode’ is to be determined—it simply seems to be at the upper end of the ‘first connecting electrode’. In particular, there is no explicit disclosure as to advantages obtained by feeding between two non-grounded points.